1. Field of the Invention
The present invention relates to a distribution control system and a distribution control method for isolating a fault section when a fault takes place on a distribution line.
2. Description of Related Art
FIG. 8 is a system diagram showing a distribution system to which a conventional distribution control system is applied. In FIG. 8, reference symbols AS/S, BS/S, CS/S, DS/S and ES/S each designate a distribution substation; F1-F9 each designate a distribution line led out of the distribution substation AS/S; F10-F18 each designate a distribution line led out of the distribution substation BS/S; F19-F26 each designate a distribution line led out of the distribution substation CS/S; F27-F34 each designate a distribution line led out of the distribution substation DS/S; F35-F43 each designate a distribution line led out of the distribution substation ES/S; and LS1-LS18 each designate a tie switch for coupling two distribution lines.
Although not shown in FIG. 8, a plurality of load break switches are interposed in each distribution line.
FIG. 9 is a block diagram showing a conventional distribution control system, in which the reference numeral 1 designates a distribution transformer of the distribution substation AS/S; 2 designates a secondary main breaker of the distribution transformer 1; and 3 designates a secondary main bus of the distribution transformer 1, from which the distribution lines F1 and F2 are drawn out.
Reference numerals 4 and 5 each designate a distribution feeder breaker; 6-11 each designate a no-voltage unopened mode load break switch; 12 designates a tie switch for coupling the distribution lines F1 and F2; 13-19 each designate a feeder terminal unit for monitoring a fault current or the like passing through the load break switches 6-11 and tie switch 12, for notifying a substation remote terminal unit 20 of presence/absence information about the fault current, and for turning on and off the load break switches 6-11 and tie switch 12 in response to a control signal from the substation remote terminal unit 20; and 20 designates the substation remote terminal unit for transferring to a control center 21 the presence/absence information about the fault current supplied from the feeder terminal units 13-19, and for transferring to the feeder terminal units 13-19 the control signal supplied from the control center 21.
The reference numeral 21 designates the control center for managing the distribution of the distribution substation AS/S; 22 designates an information collecting unit for carrying out transmission and reception of information; 23 designates a computer system for identifying a fault section from the presence/absence information supplied thereto, and for producing a control signal commanding opening of the load break switches at both ends of the fault section; and A1-A5, B1-B3 and C each designate a communication line.
FIG. 11 is a block diagram showing an internal arrangement of the load break switch and feeder terminal unit, and FIG. 12 is a diagram showing a structure of the load break switch. In FIG. 11, the reference numeral 31 designates a contact maker; 32 designates an operation rod for closing or opening the contact maker 31; 33 designates an actuator of the load break switch; 34 designates a current transformer for detecting a current; 35 and 36 each designate a control transformer for detecting a voltage; 37 designates a voltage/phase angle detector for detecting the voltage and phase on the distribution line; 38 designates a current detector for detecting a current passing through the load break switch; 39 designates a controller for monitoring an operation state of the actuator of the switch 33 and the current passing through the load break switch, and for controlling the actuator of the switch 33 in response to the control signal from the substation remote terminal unit 20; 40 designates a communication circuit for exchanging information with the substation remote terminal unit 20; 41 designates a battery for supplying power to component circuits of the feeder terminal unit in case of outage of the distribution line; and 42 designates a branch box for connecting the communication circuit 40 of the feeder terminal unit to a communication line.
In FIG. 12, the reference numeral 33a designates a movable magnetic pole attached to the operation rod 32; 33b designates a magnetic coil for driving the movable magnetic pole 33a; 33c designates a switch; 33d designates a controller for controlling the switch 33c; 33e designates a power supply of the magnetic coil 33b; 33f designates a movable rod coupled to the movable magnetic pole 33a for latching; 33g designates a latch holder; 33h designates a coil spring for opening the contact maker 31; 33i designates a spring bearing; 33j designates a coil spring for holding the latched state of the contact maker 31; 33k designates a spring bearing; 33l designates a latch control rod; 33m designates a latch operation handle; 33n designates a movable fulcrum; 33p designates a fixed fulcrum; and 33q designates a point on the latch operation handle 33m which is manually operated from the right to the left to unlatch the latch holder 33g from the movable rod 33f so that the contact maker 31 is opened by the force of the coil spring 33h.
Next, the operation of the conventional system will be described.
When controlling the distribution system of the distribution substation AS/S, the substation remote terminal unit 20 regularly transmits to the feeder terminal units 13-19 an information transmission request through the communication lines A4 and A5 so as to collect information about the load break switches 6-11 and tie switch 12 (including information as shown in FIG. 13 as well as the presence/absence information of the fault current passing through the load break switches).
Since the feeder terminal units 13-19 always collect the information about the load break switches 6-11 and tie switch 12, they send the information back to the substation remote terminal unit 20 through the communication lines A4 and A5 in response to the information transmission request from the substation remote terminal unit 20.
The information about the load break switches 6-11 and tie switch 12 thus collected by the substation remote terminal unit 20 is transferred to the control center 21, in which the computer system 23 identifies the fault section from the information about the load break switches 6-11 and tie switch 12 if a distribution line fault takes place.
Identifying the fault section, the computer system 23 supplies the substation remote terminal unit 20 with a control signal that commands opening of the load break switches at both ends of the fault section, thereby commanding the feeder terminal units managing the load break switches at both ends of the fault section to open the load break switches, and trying to isolate the fault section. To provide a precise description of a series of steps involved in this operation, it is assumed in the following that a distribution line fault takes place in the section F1-3 of the distribution line F1.
If the distribution line fault takes place in the section F1-3 of the distribution line F1 at time T1 as shown in FIG. 10, a protective relay included in the feeder breaker 4 operates so that the feeder breaker 4 trips and the distribution line F1 is shut down.
However, since the load break switches 6-8 are a non-voltage unopened mode switch, they do not open immediately even if the distribution line F1 is shut down to a non-voltage state by the distribution line fault, thereby maintaining the closed state.
Although the feeder breaker 4 automatically closes again by itself after about 60 sec. has passed since the distribution line F1 was shut down (time T4), the information about the load break switches 6-8 is transmitted to the computer system 23 in the control center 21 before that.
Since the information on the shut down of the feeder breaker 4 due to the distribution line fault is also transferred to the computer system 23 in the control center 21, the computer system 23 can recognize the occurrence of the distribution line fault.
Thus, the computer system 23 identifies the fault section from the information about the load break switches 6-8. When the distribution line fault takes place in the section F1-3, the fault current flows through the load break switches 6 and 7, but not through the load break switch 8. Using this characteristic, the computer system 23 identifies the fault section from the presence/absence information on the fault current included in the information about the load break switches 6-8.
Identifying the fault section in this way, the computer system 23 supplies the substation remote terminal unit 20 with the control signal commanding opening of the load break switches 7 and 8 at time T2 to isolate the fault section at opposite ends of the section F1-3.
Receiving the control signal commanding opening of the load break switches 7 and 8, the substation remote terminal unit 20 transfers the control signal to the feeder terminal units 14 and 15 which opens the load break switches 7 and 8.
After isolating the fault section, the computer system 23 supplies the substation remote terminal unit 20 with the control signal commanding closing of the tie switch 12 at time T3 to recover the outage of the healthy sections (although the section F1-2 is immediately charged when the feeder breaker 4 closes again at time T4, because the load break switch 6 maintains the closed state, this is not enough for the section F1-4 to be charged because the load break switch 8 is opened).
Receiving the control signal commanding closing of the tie switch 12, the substation remote terminal unit 20 transfers the control signal to the feeder terminal unit 19 which closes the tie switch 12.
After that, when the feeder breaker 4 closes again at time T4, the distribution line F1 is charged except for the fault section F1-3.
With the foregoing configuration, the conventional distribution control system can positively isolate the fault section even if a distribution line fault takes place in the distribution line F1 as long as the information about the load break switches 6-11 is transmitted to the control center 21 and the control signal of the control center 21 is transferred to the feeder terminal units 13-15 without fail. However, if a communication failure occurs between the control center 21 and the feeder terminal units 13-15, control of the load break switches 6-8 becomes impossible, which presents a problem of being unable to isolate the fault section.